On a tour through the cafeteria of Parklawn Elementary School in Alexandria, Penny McConnell points to the array of healthy foods on the day's menu: low-fat yogurt, baked chicken legs, fresh broccoli and cauliflower. As food services director for Fairfax County Public Schools, McConnell brags that the fresh green salads have become such a hit with students that teachers sneak in early to grab one before they sell out.

And then she sees him. The brown-haired boy unpacking the lunch he brought from home. Among the offerings: Gatorade and a 99-cent bag of Lay's potato chips, which by itself is 360 calories, 210 of them from fat.

"See?" she said. "This is what we're up against."

When Americans look for a scapegoat to blame for the growing childhood obesity epidemic, they often point to the schoolhouse. School officials said, however, that their efforts to promote good nutrition are thwarted by parents, who send children to school with oversized bags of chips and fight officials when they try to ban cupcakes.

Until a few years ago, the National PTA opposed federal efforts to regulate the sale of snacks and soft drinks on campuses for fear of losing the revenue. After Arkansas became the first state to require that students' body mass indexes be taken yearly, parents and some school officials argued that such measures harmed children's self-esteem and took time away from academics.

Montgomery County Council member George L. Leventhal (D-At Large) drew the ire of a local PTA for criticizing a fundraiser in which teachers worked at McDonald's. And when Fairfax County tried to do away with french fries at h igh schools last year, parents inundated the system with calls, even taking their case to the School Board. The fries were restored three days a week.

"It's not just schools," McConnell said. "We all need to be active players in this game in order to win."

But school officials, too, share in the blame.

For years, schools peddled cafeteria meals that were too high in fat and sodium. A series of reports documenting the staggering rise in childhood obesity raised alarm. The average weight for a 10-year-old boy rose to 85 in 2002 from 74 pounds in 1963, the Centers for Disease Control and Prevention said. For girls, it hit 88 pounds, up from 77 pounds.

Now, many school lunch programs have gotten rid of the deep fryers or changed to less fattening oils. They offer salad bars, whole-wheat hot dogs buns and exotic vegetables and fruits such as kiwi and jicama. The pizza crust is made of whole-wheat flour, and the hamburgers are made with black beans. Low-fat milk and 100 percent fruit juices are in.

But even where the meals have become healthier, schools continue to undercut their efforts by also selling fries and doughnuts and allowing vending machines. Exclusive contracts with soft-drink companies garner multimillion-dollar payouts for schools. Officials say the dollars buy textbooks and pay SAT fees; critics accuse schools of ignoring health consequences.

Three decades ago, the Agriculture Department tried to ban chips, cookies and soft drinks from schools but was thwarted by courts and food companies. One court ruling found that the department did not have the right to regulate foods sold outside the lunchroom. The companies argued that people, not government, should decide what they eat.

Health advocates say the situation is beginning to change, some. Fairfax County was among the first school systems in the country to limit sales of soda and snack foods. Now others, including Montgomery and the District, have followed suit.

Critics say those schools are the exceptions. "Most kids still go to school in schools where there's junk food," said Margo Wootan, nutrition policy director for the Center for Science in the Public Interest, a leading health watchdog. "If it were only a cupcake once a month, if it were only the snacks at after-care. . . . It's just that it all adds up to so much junk food, which then adds up to childhood obesity."

Parents and educators differ on how aggressively to regulate what children eat. Some parents see no harm in an occasional pizza party, but others want an all-out ban on cupcakes. Some Montgomery elementary schools still reward students with free pizzas for being good readers, while students at KIMA Public Charter School in the District staged a lunchroom boycott until they were offered a healthier menu.

Health advocates insist schools can move to more healthy offerings without dire financial consequences. Eye appeal and eatability of lunches are key. "All of us eat with our eyes," said Becky Domokos-Bays, food services director for Alexandria public schools. "Kids gravitate toward fruit. Veggies are a little harder sell."

There is evidence to back the advocates: A 2001 study at the University of Minnesota found that students would buy healthy food items if they cost less than unhealthy items. The Vista Unified School District in Oceanside, Calif., put milk, juice and water at eye level and moved soft drinks and sports beverages to lower levels to influence buying habits. They charged less for the healthy beverages. By the second year of the experiment, when they phased out soft drinks from the machines altogether, there was very little outcry. Most important, vending revenue increased.

In Philadelphia, a two-year experiment by researchers at Temple University to examine whether nutrition education combined with a change in the types of food sold at five elementary schools lowered childhood obesity rates showed extremely promising results. At the schools that banned soft drinks and candy and rewarded healthy eating with raffle tickets, children were less likely to gain weight than counterparts at other schools. Over the two years, fewer children were becoming overweight, and the number who had been overweight dropped. At schools that did not participate in the experiment, the number of overweight children increased.

More than a decade ago, when Sen. Tom Harkin (D-Iowa) proposed banning vending machines from campuses, some of the harshest criticism came from the school community. Today, such groups as the PTA are fighting alongside Harkin.

"You gotta walk the talk," National PTA President Jan Harp Domene said. "You can't just be out there for fundraising without considering" the impact on children.

Domene said PTA officials now require the fundraising vendors who attend the national convention to offer healthy fundraising alternatives in addition to candy and cookie dough.

Still, the conflict between dollars and health remains evident. In Harkin's most recent effort to regulate "competitive" foods on campuses, the PTA supported the regulations. But its members fought to include an exemption for school-approved fundraisers, such as those sponsored by booster clubs -- and groups such as their own.